The present invention relates to the general field of dynamic lubrication of an aviation turbomachine.
An aviation turbomachine has numerous elements that need to be lubricated; these include in particular rolling bearings used for supporting its shafts in rotation, and also the gears of its accessory drive gearbox.
In particular, in order to reduce friction, wear, and heating due to the high speed of rotation of the shafts of the turbomachine, the rolling bearings that support them need to be lubricated. Since simple lubrication by injecting oil solely during periods of turbomachine maintenance do not suffice, recourse is generally had to so-called “dynamic” lubrication.
Dynamic lubrication consists in putting oil into continuous circulation in a lubrication circuit. A flow of lubricating oil coming from a tank is thus delivered by a pump against the rolling elements of the bearings, which bearings are housed in enclosures that are closed by sealing gaskets. In order to avoid any leak of lubricating oil from the enclosures to the remainder of the turbomachine through the sealing gaskets, a flow of air taken from one of the compressors of the turbomachine is injected through said gaskets. The enclosures are thus pressurized relative to atmospheric pressure.
The main fraction of the air introduced into the enclosures is then discharged to the outside of the turbomachine by following a special circuit for removing oil therefrom and for controlling the pressure inside the enclosures. The lubricating oil injected into the enclosures is recovered from the bottoms of the enclosures by recovery pumps via another special circuit. In order to ensure that the enclosure is fully dried, a small fraction of the air is also sucked into these pumps and the air/oil mixture as recovered in this way needs to be separated prior to returning the de-aerated oil to the tank.
Such a lubrication method presents various drawbacks. In particular, the lubricating oil needs to be conveyed via multiple arrangements: pipes, nozzles, centrifugal scoops, centripetal scoops, crescents, channels, etc. Discharging the oil and the air carrying oil droplets also requires the use of recovery pumps and a de-oiler, thereby increasing the weight of the turbomachine.
These drawbacks are acceptable once the thermal power generated by the rolling bearings of the turbomachine is high enough to justify having recourse to such a lubrication system. This applies in particular to turbomachines in which the speed of rotation of the bearings is considerable at high power (e.g. of the order of 6000 revolutions per minute (rpm) to 8000 rpm for the low pressure shaft and of the order of 14,000 rpm to 20,000 rpm for the high pressure shaft of a two-spool turbomachine).
In contrast, when the rolling elements of one of the bearings of the turbomachine rotate at a speed that is relatively low (e.g. of the order of 1000 rpm), the power generated by the rolling elements of the bearing is too small to justify having recourse to such a lubrication system. In such a situation, it can happen that an excessive flow of lubricating oil is injected into the enclosure containing the rolling bearing that operates at a low speed of rotation, and there is a risk of oil leaking from the enclosure.